To enhance safety of a vehicle, malfunction diagnosis is executed by automatically detecting abnormality of the vehicle. The malfunction diagnosis is executed while the vehicle is traveling, i.e., while an engine electronic control unit (engine ECU) of the vehicle is running.
However, while the vehicle is traveling, vehicular states, such as an engine revolution speed, a vehicle speed, an intake air amount, an engine load, a cooling water temperature, and the like, vary too frequently for diagnosis condition to suffice. Frequency of the diagnosis thereby remains small. The engine ECU is therefore periodically diagnosed under a stable state of the vehicle while the vehicle is being parked. While the vehicle is being parked, the vehicle is not swinging or a cooling water temperature is low.
For the malfunction diagnosis during the parking, a function of periodically turning on the engine ECU while an ignition switch is turned off is provided in an in-vehicle device such as a power control device. Here, no power supply to a battery due to stopping the engine sometimes exhibits a problem.
Namely, to execute the diagnosis, an actuator must be activated, but repeatedly consuming power due to activating the actuator leads to shortage of electric voltage of the battery. Here, although decreasing power consumption of actuators used in the diagnosis can be a countermeasure to this, frequency of the diagnosis while the engine is turned off is yet limited.
In addition, a traveling state of the vehicle before being parked affects the diagnosis, so that a countermeasure to this is required. In detail, after long-hour traveling, an internal temperature of a fuel tank may remarkably increase, so that reaching a stable state of the vehicle involves a longer time interval. Here, since accurate diagnosis needs the stable state of the vehicle, a time interval for diagnosis, which is equivalent to a time interval for activating the engine ECU, must be set as being long. However, this exhibits another problem.
In detail, increasing the time interval for activating the engine ECU enables accurately detecting abnormality even after the long-hour traveling. It also enables decreasing frequency of activating the engine ECU. This results in little influence on the battery. However, decreasing frequency of diagnosis due to too long an interval makes it difficult to effectively detect abnormality.